In general, during the forming of a tire it is known to utilize plies made of unvulcanized elastomeric material internally reinforced with cords of textile, glass or metal, etc. For reasons of production economy these plies are obtained starting from a continuous piece in which the said cords constitute a kind of axial warp. This piece is subsequently reduced, by transverse cuts, into a plurality of segments which are partially superimposed over one another and then joined along the adjacent edges in such a way as to form the said plies, the opposite ends of which are then joined together on a forming drum to define a tire body or carcass.
From what has been described above it is possible to appreciate that the joining operations necessary for making a carcass are substantially of two types, the first of which involves all the operations for joining the said segments together, which are normally performed on a forming bed, and the second of which involves a single operation for joining the opposite ends of the said ply together, this being performed on the said forming drum.
All the joining operations mentioned above have until now generally been performed by means of motorized joining tools normally comprising two trains of counterposed rollers operable to clamp together the segments or the ply to be joined, and in which each train of rollers includes two rows of rollers disposed on opposite sides of a junction line. For the purpose of pressing the edges to be joined towards one another each roller of each row is disposed substantially parallel to the rollers of the corresponding row of the other train of rollers, and forms a determined angle with a corresponding roller of the other row of the same train.
The above-described known motorized tools generally form part of fixed joining installations such as, for example, those described in U.S. Pat. No. 4,231,836 or French Pat. No. 2,446,170, and are usable solely in combination with a forming table given their size and weight. As far as the joining of the ends of the plies on the forming drum are concerned, however, the small motorized tools formed for this purpose in the past, generally on the basis of what is described in British Pat. No. 1,451,831, have been quickly abandoned or converted into bed mounted tools because of their weight and bulk which is still excessive and which makes them practically impossible to use continuously, particularly for workers used to joining the plies on a forming drum. During this operation, in fact, the operator must hold the joining tool in his hand and advance it along a determined path in contact with the surface of the drum itself by performing movements which are not always easy, the repetition of which for a relatively long time becomes substantially impossible when the weight of the joining tool is more than several kilograms.
An immediate consequence of what has been described above is that, in the manufacturing industry, the flat joining on the bed is normally performed by means of motorized joining tools, while the joining on the forming drum is performed by using hand held manually operable joining tools of the type described in U.S. Pat. No. 3,909,341. Such manually operated tools, although light and simple to use, normally have the disadvantage of not forming a uniform joint both because the force with which the edges to be joined can be made to adhere depends directly on the "not always constant" force applied by the operator, and because they are normally provided with a single train of rollers acting on the outer surface of the ply.
It should be noted, in addition to what has been explained above, that in the said non-motorized tools, the presence of a single train of rollers is not due merely to structural simplification, but to the impossibility of an operator using a manually operated joining tool provided with two trains of counterposed rollers because of the friction which is developed between the rollers and the ply clamped between them. The omission of rollers in contact with the inner surface of the ply to be joined can involve an imperfect adhesion of the edges joined along the said inner surfaces of the ply and consequent rupture thereof during use.